In the process of using the food metal detector, some enterprises often pass the suspicious products removed from the production line through the channel of the food metal detector again. If they are not excluded by the instrument this time, then they think that they are qualified products and release them smoothly into the next process. In fact, this approach is unscientific. This article is the answer to the common misunderstanding: the correct way to confirm suspicious products.
1. Common misunderstandings
Generally speaking, food metal detector has two sets of coils, called vibration source; the following is composed of two opposite coils, called vibration source. When the upper coil is electrified, the magnetic field is generated, and the lower two coils accept the induced currents IA and IB. Because the coil windings are opposite, under normal conditions, A and B currents are superimposed as (ia + ib) = 0. If an object passes through, the induced current will change, resulting in unbalanced current, i.e., ia = IB = Delta i, which then forms a signal output through a circuit. However, there are some differences in the mechanism of different products through detection channels: magnetic metal takes iron as an example, it has magnetism, through magnetic field unbalance, current unbalance generated by coil A and B, Delta I generates signal output through signal amplification circuit and responds to ferrous signal; non-magnetic SUS304 as an example, metal is passing through magnetism. The field is not affected by the magnetic force line, but produces eddy current. It also causes current imbalance. Delta I generates signal output through signal amplification circuit and responds to SUS304 signal.
Semiconductor: such as brine, pure water, etc., has certain electrical properties (producing eddy current), which will affect the change of magnetic field. For example, some quick-frozen foods will have more water when frozen badly. The change of induced current is caused by magnetic field, which interferes with the normal detection of metals, and the detection rate of metal-containing products will decrease. The SUS304 signal was sent incorrectly. But some special water, salt and thick products, the increase of density, hinder the passage of magnetic lines, lead to magnetic imbalance, will missend iron signals. Therefore, there are two situations when detecting products by food metal detector. One is that the products contain metal foreign bodies, the other is caused by the interference of the components of the products themselves. If the product containing impurities passes through the food metal detector again as it is, without blockage and is judged to be released normally, it can be mixed into the normal product.
2. Misunderstanding and Doubt Resolution
When the product is removed by the food metal detector, the suspicious product should be taken out and repeated twice according to the direction of the original probe. If it can pass smoothly, it can be confirmed as qualified and flow into the normal product. If there is at least one failure in the repetition process, it can be directly determined as a non-conforming product.